Microsoft is pushing out a new test build to Windows Insiders, one that ends in ‘666’ (Build 17666) and will consume your soul if you install it. Okay, so it’s not actually demonic—we don’t think so, anyway—but it is quite literally a dark release. Or, it can be. One of the things that is new in the latest preview build is an extension of the dark theme in Windows to File Explorer, as many users have been requesting.

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“As many of you know, we added dark theme support to Windows based on your feedback. This setting is available under Settings > Personalization > Colors, and if you switch it any apps and system UI that support it will follow suit. Since releasing this feature, our top feedback request from you has been to update File Explorer to support dark theme, and with today’s build it’s happening!,” Microsoft explained in a blog post announcing the new build.

Microsoft also added dark theme support to the File Explorer context menu and Common File Dialog (Open and Save dialogs). So, if this is something you have been pining for, the latest test build is for you. Or you can wait for a polished release to arrive this fall—what’s currently being tested is Redstone 5, which is the next major upgrade to Windows 10 following the recent April 2018 Update (Redstone 4).

One thing that Microsoft notes is that as currently implemented, the dark theme in File Explorer and the Common File Dialog leaves “some unexpected light colors,” which you can see in the screenshot above. Microsoft is aware of this and is working to fix it for future test releases.

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Moving on, the latest test build also includes more of Microsoft’s Fluent Design language. Sets now have an acrylic title bar, and Microsoft has adjusted the window border so that it’s now gray. These are relatively minor additions, though little by little, Microsoft continues to tweak the way Windows looks as it works towards a more modern aesthetic.

There are various other changes in Build 17666, such as a new clipboard experience that lets you pin items, extended line endings support for Notepad, being able to search on Bing through Notepad, search previews, and a few other feature updates and additions. And of course the latest release includes a handful of general improvements and fixes, one of which was causing explorer.exe to crash every few minutes on previous builds.

The new build is available now to Windows Insiders who are subscribed the Fast ring, and also those who opted in to Skip Ahead.